<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>响应式页面</title>
    <style>
        .container{
            display: flex;
            width: 800px;
            margin: 0 auto;
            background-color: #eee;
            justify-content: center;
        }
        .item{
            width: 200px;
            border: 1px red solid;
        }
        @media screen and (max-width:700px) {
            .container{
                width: 100%;
                flex-direction: column;
            }
            .item{
                width: 100%;
            }
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="item"><h1>文档</h1></div>
        <div class="item"><h1>博客</h1></div>
        <div class="item"><h1>视频</h1></div>
    </div>
</body>
</html>